1. Field of the Invention
The present invention relates to an optical transmitter, and more particularly to an optical transmitter which transmits an information signal to be transmitted in the form of a burst signal (e.g., optical packets).
2. Description of the Background Art
FIG. 7 is a block diagram illustrating the structure of an optical transmission system including a conventional optical transmitter, in which a wavelength-tunable light source is controlled, by varying a wavelength controlling current applied thereto, so as to output light packets of different wavelengths in a time-divided manner (so that the wavelength will be different from optical packet to optical packet). Hereinafter, this conventional optical transmission system will be described with reference to FIG. 7.
In FIG. 7, the conventional optical transmission system comprises an optical transmitter 1000, an optical transmission means 2000, and optical receivers 2041 to 204n. The optical transmitter 1000 includes a data unit 1010, a wavelength information processing unit 1020, a wavelength-tunable light source 1030, and an optical modulation unit 1040. The optical transmission means 2000 includes an optical transmission path 2010, an optical amplifier 2020, and a wavelength router 2030.
In the optical transmission system having the above structure, the data unit 1010 outputs an information signal, which is to be transmitted in the form of optical packets, and wavelength information representing a wavelength of each optical packet. In accordance with the wavelength information outputted from the data unit 1010, the wavelength information processing unit 1020 applies a predetermined wavelength controlling current to the wavelength-tunable light source 1030, with respect to each optical packet. As a result, the wavelength-tunable light source 1030 outputs light having a wavelength corresponding to the wavelength controlling current outputted from the wavelength information processing unit 1020. The optical modulation unit 1040 modulates the light outputted from the wavelength-tunable light source 1030 with the information signal outputted from the data unit 1010. Thus, optical packets are generated and outputted.
The optical amplifier 2020 amplifies the optical packets which have been outputted from the optical modulation unit 1040 and transmitted over the optical transmission path 2010. The wavelength router 2030 includes a plurality of output ports, and depending on the wavelengths of the optical packets which have been outputted from the optical amplifier 2020, separately outputs the optical packets through different output ports. The optical receivers 2041 to 204n, which are provided respectively corresponding to the plurality of output ports of the wavelength router 2030, convert the optical packets outputted from the wavelength router 2030 into electric signals (information signals). The optical amplifier 2020 may alternatively be inserted between the wavelength router 2030 and the optical receivers 2041 to 204n. 
However, in accordance with the above-described conventional optical transmission system, if an intermittent optical signal (optical packets) as shown in (a) of FIG. 8 is inputted to the optical amplifier 2020, the output optical signal from the optical amplifier 2020 will experience an instantaneous increase inthe optical signal level (known as an “optical surge”), thereby causing a waveform degradation as illustrated in (b) of FIG. 8. An optical surge is known to occur due to transient response characteristics which exist, when an optical signal is inputted after a long no-data period, for reasons associated with the physiological properties and/or construction of the optical amplifier 2020, e.g., its relaxation time constant. If the optical signal has such a level fluctuation over time, the optimum identification level at each optical receiver will also fluctuate with the level fluctuation. As a result, there is a problem in that in a structure where data is to be identified at an optical receiver against a prefixed identification level, it is difficult to constantly obtain optimum transmission characteristics.